package dycaps

import (
	"crypto/sha256"
	"encoding/binary"
	"fmt"
	"math/big"
)

// KZGParams KZG参数结构
type KZGParams struct {
	// 群参数
	G1 []byte `json:"g1"`
	G2 []byte `json:"g2"`
	
	// 可信设置参数
	TrustedSetup []byte `json:"trusted_setup"`
	
	// 域参数
	FieldSize *big.Int `json:"field_size"`
}

// KZGCommitment KZG承诺结构
type KZGCommitment struct {
	Commitment []byte `json:"commitment"`
	Degree     int    `json:"degree"`
}

// KZGWitness KZG见证结构
type KZGWitness struct {
	Witness []byte `json:"witness"`
	Index   int    `json:"index"`
	Value   []byte `json:"value"`
}

// RealKZG 真实KZG实现（占位，实际需要集成KZG库）
type RealKZG struct {
	params *KZGParams
}

// NewRealKZG 创建真实KZG实例
func NewRealKZG(params *KZGParams) *RealKZG {
	return &RealKZG{
		params: params,
	}
}

// Commit 提交多项式
func (k *RealKZG) Commit(coefficients []byte) ([]byte, error) {
	// 这里应该使用真实的KZG库实现
	// 目前使用占位实现
	hash := sha256.Sum256(coefficients)
	return hash[:], nil
}

// CreateWitness 创建见证
func (k *RealKZG) CreateWitness(commitment []byte, index int, value []byte) ([]byte, error) {
	// 这里应该使用真实的KZG库实现
	// 目前使用占位实现
	witnessData := append(commitment, byte(index))
	witnessData = append(witnessData, value...)
	hash := sha256.Sum256(witnessData)
	return hash[:], nil
}

// VerifyEval 验证评估
func (k *RealKZG) VerifyEval(commitment []byte, index int, value []byte, witness []byte) bool {
	// 这里应该使用真实的KZG库实现
	// 目前使用占位实现
	expectedWitness, err := k.CreateWitness(commitment, index, value)
	if err != nil {
		return false
	}
	return string(expectedWitness) == string(witness)
}

// Polynomial 多项式结构
type Polynomial struct {
	Coefficients []*big.Int `json:"coefficients"`
	Degree       int        `json:"degree"`
}

// NewPolynomial 创建新多项式
func NewPolynomial(degree int) *Polynomial {
	coeffs := make([]*big.Int, degree+1)
	for i := range coeffs {
		coeffs[i] = big.NewInt(0)
	}
	return &Polynomial{
		Coefficients: coeffs,
		Degree:       degree,
	}
}

// SetCoefficient 设置系数
func (p *Polynomial) SetCoefficient(index int, value *big.Int) error {
	if index < 0 || index > p.Degree {
		return fmt.Errorf("index %d out of range [0, %d]", index, p.Degree)
	}
	p.Coefficients[index] = new(big.Int).Set(value)
	return nil
}

// Evaluate 评估多项式
func (p *Polynomial) Evaluate(x *big.Int) *big.Int {
	result := big.NewInt(0)
	power := big.NewInt(1)
	
	for i := 0; i <= p.Degree; i++ {
		term := new(big.Int).Mul(p.Coefficients[i], power)
		result.Add(result, term)
		power.Mul(power, x)
	}
	
	return result
}

// Serialize 序列化多项式
func (p *Polynomial) Serialize() ([]byte, error) {
	// 使用相同的序列化函数
	data := make([]byte, 0)
	
	// 写入度数
	degreeBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(degreeBytes, uint32(p.Degree))
	data = append(data, degreeBytes...)
	
	// 写入系数
	for _, coeff := range p.Coefficients {
		coeffBytes := coeff.Bytes()
		// 写入系数长度
		lenBytes := make([]byte, 4)
		binary.BigEndian.PutUint32(lenBytes, uint32(len(coeffBytes)))
		data = append(data, lenBytes...)
		// 写入系数数据
		data = append(data, coeffBytes...)
	}
	
	return data, nil
}

// Deserialize 反序列化多项式
func DeserializePolynomial(data []byte) (*Polynomial, error) {
	if len(data) < 4 {
		return nil, fmt.Errorf("insufficient data for polynomial")
	}
	
	// 读取度数
	degree := int(binary.BigEndian.Uint32(data[:4]))
	offset := 4
	
	p := NewPolynomial(degree)
	
	// 读取系数
	for i := 0; i <= degree; i++ {
		if offset+4 > len(data) {
			return nil, fmt.Errorf("insufficient data for coefficient %d", i)
		}
		
		// 读取系数长度
		coeffLen := int(binary.BigEndian.Uint32(data[offset : offset+4]))
		offset += 4
		
		if offset+coeffLen > len(data) {
			return nil, fmt.Errorf("insufficient data for coefficient %d data", i)
		}
		
		// 读取系数数据
		coeffBytes := data[offset : offset+coeffLen]
		offset += coeffLen
		
		coeff := new(big.Int).SetBytes(coeffBytes)
		p.SetCoefficient(i, coeff)
	}
	
	return p, nil
}

// Share 份额结构
type Share struct {
	Index int      `json:"index"`
	Value *big.Int `json:"value"`
	Proof []byte   `json:"proof,omitempty"`
}

// SerializeShare 序列化份额
func SerializeShare(share *Share) ([]byte, error) {
	// 使用相同的序列化函数
	data := make([]byte, 0)
	
	// 写入索引
	indexBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(indexBytes, uint32(share.Index))
	data = append(data, indexBytes...)
	
	// 写入值
	valueBytes := share.Value.Bytes()
	valueLenBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(valueLenBytes, uint32(len(valueBytes)))
	data = append(data, valueLenBytes...)
	data = append(data, valueBytes...)
	
	// 写入证明（如果有）
	if len(share.Proof) > 0 {
		proofLenBytes := make([]byte, 4)
		binary.BigEndian.PutUint32(proofLenBytes, uint32(len(share.Proof)))
		data = append(data, proofLenBytes...)
		data = append(data, share.Proof...)
	} else {
		// 写入0长度
		proofLenBytes := make([]byte, 4)
		binary.BigEndian.PutUint32(proofLenBytes, 0)
		data = append(data, proofLenBytes...)
	}
	
	return data, nil
}

// DeserializeShare 反序列化份额
func DeserializeShare(data []byte) (*Share, error) {
	if len(data) < 8 {
		return nil, fmt.Errorf("insufficient data for share")
	}
	
	offset := 0
	
	// 读取索引
	index := int(binary.BigEndian.Uint32(data[offset : offset+4]))
	offset += 4
	
	// 读取值长度
	valueLen := int(binary.BigEndian.Uint32(data[offset : offset+4]))
	offset += 4
	
	if offset+valueLen > len(data) {
		return nil, fmt.Errorf("insufficient data for share value")
	}
	
	// 读取值
	valueBytes := data[offset : offset+valueLen]
	offset += valueLen
	
	value := new(big.Int).SetBytes(valueBytes)
	
	// 读取证明长度
	proofLen := int(binary.BigEndian.Uint32(data[offset : offset+4]))
	offset += 4
	
	var proof []byte
	if proofLen > 0 {
		if offset+proofLen > len(data) {
			return nil, fmt.Errorf("insufficient data for share proof")
		}
		proof = data[offset : offset+proofLen]
	}
	
	return &Share{
		Index: index,
		Value: value,
		Proof: proof,
	}, nil
}

// Interpolate 拉格朗日插值
func Interpolate(shares []*Share, x *big.Int) (*big.Int, error) {
	if len(shares) == 0 {
		return nil, fmt.Errorf("no shares provided")
	}
	
	result := big.NewInt(0)
	
	for i, share := range shares {
		// 计算拉格朗日基多项式
		lagrange := big.NewInt(1)
		
		for j, otherShare := range shares {
			if i != j {
				// 计算 (x - x_j) / (x_i - x_j)
				numerator := new(big.Int).Sub(x, big.NewInt(int64(otherShare.Index)))
				denominator := new(big.Int).Sub(big.NewInt(int64(share.Index)), big.NewInt(int64(otherShare.Index)))
				
				// 计算模逆
				// 使用secp256k1素数
				secp256k1Prime := new(big.Int)
				secp256k1Prime.SetString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F", 16)
				denomInv := new(big.Int).ModInverse(denominator, secp256k1Prime)
				if denomInv == nil {
					return nil, fmt.Errorf("modular inverse does not exist")
				}
				
				term := new(big.Int).Mul(numerator, denomInv)
				lagrange.Mul(lagrange, term)
			}
		}
		
		// 累加 share.Value * lagrange
		term := new(big.Int).Mul(share.Value, lagrange)
		result.Add(result, term)
	}
	
	return result, nil
}
